What FIREs Up Star Formation? The Emergence of Kennicutt- Schmidt from Feedback

What FIREs Up Star Formation? The Emergence of Kennicutt- Schmidt from Feedback SFDE7, Quy Nhon, Vietnam August, 7 Matt Orr Ph.D. Advisor: Dr. Philip F. Hopkins TAPIR California Institute of Technology Pasadena, CA

Why the scatter and slope of the KS law? Linear to quadratic slope & ~- dex scatter, dependent on Σ gas Why? Bigiel et al. 8 Kennicutt & Evans

What do we expect from feedback in equilibrium? Low Gas Surface Density: Thermal Support Heating = Cooling (See Hayward & Hopkins 5, Ostriker et al. ) (See Faucher-Giguere et al., Ostriker & Shetty ) High Gas Surface Density: Turbulent Support Momentum from SNe = Turbulent Dissipation in ISM

Where we come in: Simulations FIRE: Feedback In Realistic Environments GIZMO/Gadget SPH Code Includes all the feedback we need! Cosmological, 9 - M halos Mass resolution ~ - 4 M Multiphase ISM > Consequential Feedback Physics Collaboration Site: http://fire.northwestern.edu/

Star Formation on FIRE (At the smoothing length scale ~few pc) Rules for star formation in gas: Gas Collaboration Site: http://fire.northwestern.edu/

Star Formation on FIRE (At the smoothing length scale ~few pc) Rules for star formation in gas: Gas is dense, n crit (~ cm - ). Dense Gas Collaboration Site: http://fire.northwestern.edu/

Star Formation on FIRE (At the smoothing length scale ~few pc) Rules for star formation in gas: Gas is dense, n crit (~ cm - ). Predominantly molecular in nature, i.e. f H > /. Dense H Gas Collaboration Site: http://fire.northwestern.edu/

Star Formation on FIRE (At the smoothing length scale ~few pc) Rules for star formation in gas: Gas is dense, n crit (~ cm - ). Predominantly molecular in nature, i.e. f H > /. Dense H Gas Is locally gravitationally bound Collaboration Site: http://fire.northwestern.edu/

Star Formation on FIRE (At the smoothing length scale ~few pc) Rules for star formation in gas: Gas is dense, n crit (~ cm - ). Predominantly molecular in nature, i.e. f H > /. Dense Gas Is locally gravitationally bound Then: Collaboration Site: http://fire.northwestern.edu/ where: locally % efficient star formation

Star Formation on FIRE (At the smoothing length scale ~few pc) Rules for star formation in gas: Gas is dense, n crit (~ cm - ). Predominantly molecular in nature, i.e. f H > /. Dense Gas Feedback presumably acts here Is locally gravitationally bound Then: Collaboration Site: http://fire.northwestern.edu/ where: locally % efficient star formation

Back to KS: Galaxy Maps Face-on projection Halos from: Hopkins et al. 4, Chan et al. 5, Feldmann et al. 6 (Not FIRE.. NCG )

Back to KS: Galaxy Maps Pixel sizes pc - 5 kpc Mock observational maps of various quantities (Gas, SFR, Ω dyn )

Kennicutt-Schmidt is there! Neutral Hydrogen Cold & Dense Gas kpc pixels Myr Avg SFR ~ Hα log( SFR [M yr kpc ]) 4 ~HI + H ~H Observational Data Range Observational Data Range log( gas [M pc ]) log( gas [M pc ]) Cold & Dense ~ < K, >/cc Likely an underestimate by ~/ dex Observations from Kennicutt (998), Kennicutt, Jr. et al. (7), Bigiel et al. (8), Bothwell et al. (), Boquien et al. (), Daddi et al. (), Verley et al. (), and Lisenfeld et al. (), Genzel et al. (), Onodera et al. (), and Shi et al. ().

No apparent redshift dependence Neutral Hydrogen Cold & Dense Gas Myr Avg SFR ~ Hα log( SFR [M yr kpc ]) 4 z 6 z z z<.5 kpc pixels ~HI + H ~H 4 log( gas [M pc ]) No apparent dependence 4 log( gas [M pc ]) Observations from Kennicutt (998), Kennicutt, Jr. et al. (7), Bigiel et al. (8), Bothwell et al. (), Boquien et al. (), Daddi et al. (), Verley et al. (), and Lisenfeld et al. (), Genzel et al. (), Onodera et al. (), and Shi et al. ().

There is a weak metallicity dependence Neutral Hydrogen Cold & Dense Gas Myr Avg SFR ~ Hα log( SFR [M yr kpc ]) 4 <Z <.. <Z <.5.5 <Z < <Z kpc pixels ~HI + H ~H 4 log( gas [M pc ]) 4 log( gas [M pc ]) Large overlap, but systematic average dependence Observations from Kennicutt (998), Kennicutt, Jr. et al. (7), Bigiel et al. (8), Bothwell et al. (), Boquien et al. (), Daddi et al. (), Verley et al. (), and Lisenfeld et al. (), Genzel et al. (), Onodera et al. (), and Shi et al. ().

Z Dependence is Consistent with Expectation from SNe Feedback log( SFR/h SFRi) (~HI + H ) log gas Bins [.,.] [.,.45] [.45,.6] [.6,.75] [.75,.] [.,.4] Close-ish to SNe Feedback s Z dependence ~/4 (Cioffe 988) Upturn at high metallicity log(z/z ) Weak SFR~ Z /4ish dependence.

Dynamical Times correlate more strongly than metallicity Neutral Hydrogen Cold & Dense Gas Myr Avg SFR ~ Hα log( SFR [M yr kpc ]) 4 < 9 < < 9 < 5 5 < 9 < 5 5 < 9 < < 9 kpc pixels ~HI + H ~H 4 log( gas [M pc ]) 4 log( gas [M pc ]) Much more strongly, when dynamical timescale ~ feedback timescale Observations from Kennicutt (998), Kennicutt, Jr. et al. (7), Bigiel et al. (8), Bothwell et al. (), Boquien et al. (), Daddi et al. (), Verley et al. (), and Lisenfeld et al. (), Genzel et al. (), Onodera et al. (), and Shi et al. ().

/t dyn Dependence is nearly linear log( SFR/h SFRi).5..5..5..5. (~HI + H )..5..5 log( [Gyr ]) log gas Bins [.,.] [.,.45] [.45,.6] [.6,.75] [.75,.] [.,.4] ~Linear dependence Close to expectation value of turbulent equilibrium Momentum injection from young stars ~turbulent momentum injection Strong SFR~ /Dynamical Time dependence.

Not far from predicted equilibrium SFRs log( SFR [M yr kpc ]) 4 5 FIRE Simulations High gas Prediction Low gas Prediction kpc pixels Pixel-to-pixel comparison Log difference between High Surf. Dense Predict and actual Myr SFR Log difference between Low Surf. Dense Predict and actual Myr SFR log( SFR) [dex] log( SFR) [dex].5..5..5..5 log( gas [M pc ]) Only ~/ dex out of turbulent equilibrium

Not far from predicted equilibrium SFRs log( SFR [M yr kpc ]) Constant ~ dex scatter 4 kpc pixels may 5 be entirely Log difference between High Surf. Dense Predict and actual Myr SFR Orr et al (in prep) to explore. Log difference between Low Surf. Dense Predict and actual Myr SFR log( SFR) [dex] log( SFR) [dex] FIRE Simulations High gas Prediction Low gas Prediction.5..5..5..5 log( gas [M pc ]) Pixel-to-pixel comparison non-equilibrium effects? Only ~/ dex out of turbulent equilibrium

KS is not smooth in time. HI+H gas pc pixels kpc pixels mv mi

KS is not smooth in time. HI+H gas pc pixels kpc pixels mq A weird one.. small gas disk, aligned with stellar disk face-on, and a large ~ kpc radius gas stream. Has a particularly largely varying KS relation

Efficiencies? How many dynamical times in a depletion time? Low Gas Surface Density High Gas Surface Density Very low gas surface densities Which should roughly be a constant too

Roughly constant efficiencies Neutral Hydrogen Cold & Dense Gas kpc pixels Myr Avg SFR ~ Hα log( SFR [M yr kpc ]) 4 = =. =. ~HI + H ~H Observational Data Range Observational Data Range log( gas [M yr kpc ]) log( gas [M yr kpc ]) Effective efficiency per dynamical time is less than ~% Observations from Kennicutt (998), Daddi et al. (), Kennicutt, Jr. et al. (7) & Genzel et al. ()

No redshift dependence Myr Avg SFR ~ Hα log( SFR [M yr kpc ]) 4 = =. =. z 6 z z z<.5 Neutral Hydrogen kpc pixels ~HI + H ~H Cold & Dense Gas log( gas [M yr kpc ]) log( gas [M yr kpc ]) Lots of scatter, but no separation. Observations from Kennicutt (998), Daddi et al. (), Kennicutt, Jr. et al. (7) & Genzel et al. ()

No metallicity dependence here! Myr Avg SFR ~ Hα log( SFR [M yr kpc ]) 4 = =. =. <Z <.. <Z <.5.5 <Z < <Z Neutral Hydrogen kpc pixels ~HI + H ~H Cold & Dense Gas log( gas [M yr kpc ]) log( gas [M yr kpc ]) Lots of scatter, but no separation. Observations from Kennicutt (998), Daddi et al. (), Kennicutt, Jr. et al. (7) & Genzel et al. ()

Summary Kennicutt-Schmidt emerges as a time and spatially averaged equilibrium between star formation and feedback processes in the FIRE simulations. Weak metallicity dependence, linear /t dyn dependence ~- dex ± sigma scatter appears intrinsic, nonequilbium?.efficiencies in the -% range, no apparent metallicity/dynamical time dependencies. THANKS FOR LISTENING